Basic and applied biological research and biotechnology are limited by the ability to get information into and from living systems and to act on information inside living systems. For example, there are only a small number of inducible promoter systems available to provide control over gene expression in response to exogenous molecules. Many of the molecular inputs to these systems are not ideal for broad implementation, because they can be expensive and introduce undesired pleiotropic effects. In addition, broadly applicable methods for getting information from cells noninvasively have been limited to strategies that rely on protein and promoter fusions to fluorescent proteins, which enable researchers to monitor protein levels and localization and transcriptional outputs of networks, leaving a significant amount of the cellular information content currently inaccessible.
Moreover, monitoring the status of a complex biological system usually entails simultaneous tracking and responding to a plurality of input signals, such as the presence/absence/concentration of specific molecules or metabolites. The ability to detect and respond to status change of the individual signals is desirable for any complex biological system.